Sorted in order of importance:
Suspension
Wheels
Transmission
Breaks
Body & Engine

I recommend Tuning at the airport as it gives you good options surrounding the area for test roads for Drift and grip builds.

Special Thanks to Sakura commander for helping with some Info and testing.

Camber:
RWD = Negative Front, Neutral Rear (drift can benefit from some Negative Rear for Traction)
FWD = Neutral to Negative Front, Negative Rear

Caster Angle:
Lower Angle = Snappy inputs, Tighter corners, good for Drift Transitions
Higher Angle = Stable at Speed, Slower Steering
6-7 Degrees for most cars is typically ok

Ackerman Angle:
Grip racing = Values closer to 100%
Drifting = Preference, Values closer to 0% (More Ackerman angle can be beneficial depending on your preference.)

Steering Angle:
Grip racing = LOWEST (Preference, in game more steering angle = smaller inputs on your controller)
Drifting = MAX

Toe:
Grip racing = 0 to -0.2 Front, 0 Rear
Drifting = Negative front, Slight Toe in Rear

Spring stiffness:
If your car over-steers, make the front suspension stiffer and/or the rear one softer
If your car under-steers, make the front suspension softer and/or the rear one stiffer

Damper:
Slow includes braking, accelerating, making transitions
Fast includes hitting road bumps and other imperfections
This is all preference

Spring Length:
Lower typically (Preference)

Sway Bar/ Anti Roll bar:
Biggest contributor to under or over steer,
If your car under-steers, make front softer and back stiffer
If your car over-steers, make front stiffer and back softer

Rims marked as follows: 235/40 R19.

235 is the rim width in mm.
40 is the profile of the tire used with this rim in mm.
R19 is the diameter of the rim. In our case 19 inches.

Simplified:
Smaller diameter - faster acceleration, lighter input, lower top speed.
Bigger diameter - bigger top speed, slower acceleration, heavier input.

Tires are available in two versions: Racing and Elite.

Simplified:
Racing = Grip
Elite = Drift

Lower pressure = Better acceleration, Worse Breaks, Worse handling
Higher Pressure = Worse Acceleration, Better breaks, Better Handling

* Some AWD cars that under-steer will benefit from elite tires. Try and see what you prefer the feel of.

Tires to use in game are a preference. Personally I like Street+ for Drift and Racing+ for Grip.

T50S swap when you are looking for absolute best performance if u can afford it. Purple Gearbox can always tune higher


Difflocking: (Racing Diff Only)
Grip: 0.7-0.13 (More locked, the faster you will exit the corners, but the risk of losing traction is higher)
Drift: Welded or fully locked

Lock acceleration (Elite and Ultimate Diff Only):
If you over-steer when on the throttle, Increasing this setting can help

Lock Coast (Elite and Ultimate Diff Only):
In you under-steer on corner entry (off throttle) Decreasing this can help.

Preload (Elite and Ultimate Diff Only):
Higher setting = Quicker diff locking

Final Drive:
The final drive adjusts the overall length of all gears, without altering the ratios of every gear individually.
Bigger values mean shorter gears, lower values mean longer gears.

Gears:
Bigger values mean shorter gear, smaller values mean longer gears.
This Takes forever to get Jussssst right, you have to adjust to preference and run the car each time

Front brake bias:
Grip: slightly more front based than your weight balance, EX: F45-55R balance car wants around (47/49 Front) VS (Rear 53/51) brake balance
Drift: MAXED

Break Force:
More here = Quicker stop, fine tune for your build by running the car.

Totally up to you, keep it in the class, Change everything or Nothing at all.

With small exception of body weight reduction and aero for acceleration and grip. You can always add weight back in by tuning and buying larger fuel tank to not go up in classes.